1. Field of the Invention
The present invention relates to a capacitance sensing circuit and a power providing apparatus, and particularly relates to a capacitance sensing circuit and a power providing apparatus utilizing a voltage holding circuit.
2. Description of the Prior Art
A recent electronic apparatus always comprises a touch control apparatus. For example, the major input mechanism for a smart phone is that a user can utilize an object such as a finger or a touch control pen to input a command. The touch control panel for a laptop is also another kind of a touch control apparatus. The touch control apparatus can be classified into various types, and a popular one there between is a capacitor type touch control apparatus. Such kind of touch control apparatus determines the touch control operation for the object depending on the variation of the capacitance value.
FIG. 1 is a circuit diagram for a prior art capacitance sensing circuit. As shown in FIG. 1, the voltage source Vu charges the sensing capacitor CS, such that the voltage of the sensing terminal TS is kept at a predetermined voltage VP. If the object approaches or touches an electronic apparatus which the capacitance sensing circuit is provided in, a capacitance value of the sensing capacitor CS increases such that the voltage of the sensing terminal TS is reduced to be smaller than the predetermined voltage VP, and thereby the output for the comparator Com changes. By this way, it can be determined that if the object approaches or touches the electronic apparatus which the capacitance sensing circuit is provided in.
However, the sensing capacitor CS may have leakage current after it is charged to the predetermined voltage VP, thus the voltage of the sensing terminal TS decreases. In such case, the comparator Com may wrongly determines the object approaches or touches even the object is far away, since the voltage of the sensing terminal TS decreases.